modem/msm-modem{,-wwan-port}: move to a seperate repository

Moved them to a seperate repository with meson as buildsystem. That makes it much more maintainable in a single repository, suitable for upstreaming in Alpine, allows other distros to use it, and cleans up A LOT of tech dept.

See https://gitlab.postmarketos.org/fossdd/msm-modem & https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/95316

TODO:

• Add now missing post-install scripts for openrc services of rmtfs, msm-modem-uim-selection, msm-modem-wwan-port
• Move https://gitlab.postmarketos.org/fossdd/msm-modem to https://gitlab.postmarketos.org/postmarketOS
• Make @barni2000 (current msm-modem-wwan-port maintainer) co-maintainer of the msm-modem repo, if they agree
• Merge https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/95316
• Merge this